1. Field
The general inventive concept relates to a surface acoustic wave sensor system and, more particularly, to a surface acoustic wave sensor system having substantially reduced signal interference and noise between unit surface acoustic wave sensors therein.
2. Description of the Related Art
A surface acoustic wave (“SAW”) is a mechanical wave (as opposed to an electromagnetic wave, for example,) that is generated from movements of particles by external thermal, mechanical and/or electrical forces. More particularly, a SAW is propagated by vibration energy, most of which is concentrated on a surface of a medium that propagates the SAW. A SAW sensor is a device that senses, e.g., detects, a target material, such as an analyte, using a SAW.
Generally, the SAW sensor is disposed on a substrate made of a piezoelectric material, and includes a receptor that binds to a specific target material on a surface of the SAW sensor. Thus, when a solution, which contains the target material, flows to the SAW sensor, a wavelength is changed by physical, chemical and/or electrical reactions between the target material and the receptor. The resulting change is used to diagnose and monitor the contents of the target material.
The SAW sensor is particularly sensitive to a pressure of a liquid, as well as to viscosity or density of a medium (such as the liquid), and corresponding mass changes on the surface of the SAW sensor. Accordingly, precise control of the liquid is desired to minimize noise, which is a signal change due to factors other than the above-mentioned factors that are used to diagnose and monitor the target material.
In a typical SAW sensor, an oscillation technique or method of applying an output signal, which is emitted from an output inter-digital transducer (“IDT”), to an input IDT of the SAW sensor is used to generate a SAW in an electrode of the SAW sensor. In addition, in the oscillation method, a technique of generating a specific frequency outside the SAW sensor includes applying the specific frequency to the input IDT, and plotting an emitted output signal of the SAW sensor.
The oscillation method has an improved sensitivity over other methods. However, to use the oscillation method, an oscillator is required to be installed in the SAW sensor. The oscillator is generally in contact with and parallel to the SAW sensor.
Since large changes may occur in the SAW sensor, due to pressure gradients needed for fluid flow, for example, a technique and apparatus that reduces an error caused by this pressure is required when the SAW sensor is used.